Exhaust system with heat accumulator

ABSTRACT

An exhaust system for a combustion engine includes an exhaust pipe, and a heat accumulator housing in surrounding relationship to the exhaust pipe. Arranged in the heat accumulator housing are heat pipes to provide a heat transport of heat energy contained in exhaust gas. Heat energy thus withdrawn from the exhaust gas can be carried off via the heat pipes in the heat accumulator housing.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims the priority of German Patent Application, Serial No. 10 2011 103 109.3, filed May 25, 2011, pursuant to 35 U.S.C. 119(a)-(d), the content of which is incorporated herein by reference in its entirety as if fully set forth herein.

BACKGROUND OF THE INVENTION

The present invention relates to an exhaust system for a combustion engine.

The following discussion of related art is provided to assist the reader in understanding the advantages of the invention, and is not to be construed as an admission that this related art is prior art to this invention.

Combustion engines, e.g. Otto engines or Diesel engines, consume fuels for operation. As oil reserves are limited, it is desired to maximize performance of a combustion engine and thus exploitation of energy contained in the fuel. Due to the Carnot process, the efficiency of a combustion engine for converting energy contained in the fuel into mechanical energy is however limited to 40%. In other words, ⅔ of chemical energy bound in fuel is not available for the actual purpose of the combustion engine, i.e. conversion of chemical energy into mechanical energy, but is lost as loss energy. In order to be able to still exploit this energy, especially in the automobile industry, there are many approaches to, for example, recover heat energy or energy bound in the exhaust and to supply it for an appropriate purpose. For example, the heat energy can be used for heating the passenger compartment. Other approaches involve the use of thermoelectric generators to convert heat energy, contained in the exhaust, into electric energy which, in turn, can be utilized for operation of a motor vehicle.

In order to operate a combustion engine in an optimum efficiency range, optimal operating conditions have to be established. The combustion engine which predominantly is made from metallic material is designed in a way as to run efficiently enough at operating temperature. In other words, the different thermal expansions of engine block, pistons, piston rings, cylinder head, valves and further components are suited to one another in such a way as to realize optimal efficiency at an average operating temperature of the core components at about 90° to 100° C., and at this operating temperature the engine performance is minimized and the charge cycle is optimized. Also automotive fluids of a combustion engine, e.g. engine oil, or in downline transmissions, the mechanical components as well as transmission oils are optimized for use at the respective operating temperature.

In particular when cold-start phases are involved which take place even at a starting temperature of 20° C., but also at starting temperatures of 0° C. or minus degrees, it is therefore necessary to quickly heat the individual components to operating temperature. Various approaches have been proposed heretofore to recover heat energy of the exhaust gas by withdrawing heat contained in the exhaust and feeding it to the desired site. This requires, however, the use of heat exchangers in the region of the exhaust tract, causing a rise in the exhaust-gas back pressure so that the overall efficiency of the combustion engine is adversely affected.

The tendency to increasingly minimize exhaust emission and thus accompanying exhaust after-treatment components, e.g. particle filter or catalytic converter, runs counter however to the removal of heat from the exhaust gas during the cold-start phase because the exhaust after-treatment systems require also heat energy to ensure their full effect. Moreover, oftentimes a heat transfer medium, especially water, is used that in turn limits however efficiency and thus results in an inadequate solution.

It would be desirable and advantageous to provide an improved exhaust system to obviate prior art shortcomings and to allow a targeted heat transport without removing from the exhaust gas excessive amount of heat energy in certain operating situations.

SUMMARY OF THE INVENTION

According to one aspect of the present invention, an exhaust system for a combustion engine includes an exhaust pipe, a heat accumulator housing in surrounding relationship to the exhaust pipe, and heat pipes arranged in the heat accumulator housing to provide a heat transport of heat energy contained in exhaust gas.

The present invention resolves prior art problems by arranging a heat accumulator about part of the exhaust system, e.g. about at least a region of an exhaust-carrying pipe of the exhaust tract. The heat accumulator can be designed in the form of a heat accumulator housing to completely surround or envelope the exhaust pipe at least in a region thereof in flow direction of the exhaust gas. Heat pipes can be integrated in the heat accumulator to establish a connection to a heat sink, advantageously to a component to which heat is intended to be supplied.

In particular during cold-start performance, heat from the heat accumulator is used to heat connected components. In other words, no energy is removed from the exhaust gas during the cold-start phase so that the exhaust system according to the present invention can be arranged upstream of an exhaust gas after-treatment unit as well as downstream of an exhaust gas after-treatment unit. The performance of the exhaust gas after-treatment unit is not, or only insignificantly, impacted by an exhaust system according to the present invention.

By arranging the heat accumulator about the exhaust pipe in accordance with the present invention, there is no need to integrate any elements in the exhaust gas tract, i.e. inside the exhaust pipe. Thus, there is no increase in the exhaust-gas back pressure. When the overall system of the combustion engine has reached its optimum operating temperature, heat energy contained in the exhaust gas can be used to charge the heat accumulator in the absence of any adverse effect on the exhaust gas after-treatment unit or other elements disposed in the exhaust tract.

According to another advantageous feature of the present invention, the exhaust pipe may be completely surrounded by the heat accumulator housing. The heat accumulator housing may be configured in the form of a cladding tube, sized to completely envelope the exhaust pipe at least in a region thereof.

According to another advantageous feature of the present invention, the heat accumulator housing, in particular the heat accumulator located therein, may be made from a zeolite. Dry zeolite removes water vapor from ambient air as a result of its hygroscopic character. The attachment of water molecules to the surface of the zeolite causes the molecule to transform to an energetically lower state. Water vapor thus gives off energy in the form of heat to the zeolite, causing the zeolite in turn to intensely heat up. This heat is then carried away by heat pipes arranged in the heat accumulator housing. The supply of heat energy from the exhaust onto the zeolite, in turn, desorbs water molecules above a certain temperature and the zeolite is returned to its dry initial state.

According to another advantageous feature of the present invention, a heat storage medium can be provided in the heat accumulator housing, with the heat storage medium being made of a material that includes zeolite.

Through selection of a zeolite material and dimensioning of the heat accumulator housing, the exhaust system according to the present invention can be best suited to the cold-start performance of the combustion engine for which the exhaust system is intended for use. In addition, active or passive open-loop and closed-loop control of the exhaust system is conceivable by which the exhaust system can be further modified to the respective operating state to be adjusted.

According to another advantageous feature of the present invention, the heat pipes can be arranged in the zeolite. Advantageously, the heat pipes can be completely surrounded by the zeolite. In other words, the heat pipes are fully enclosed in the heat accumulator housing. The heat pipes emerge from the heat accumulator housing only in the connection zone, advantageously an end region of the heat pipes, in order to be able to carry heat out of the heat accumulator housing.

According to another advantageous feature of the present invention, the heat pipes can be arranged in parallel relationship to an exhaust-gas flow direction. It thus becomes possible to use especially short distances to conduct heat energy removed from the exhaust into the heat pipes and from there to carry it off via fluid located in the heat pipes. Thus, heat energy can be removed from the exhaust over a length of 50, 100 or also 200 mm and transferred by heat conduction through the heat accumulator housing into the heat pipe and carried off from there.

According to another advantageous feature of the present invention, several of the heat pipes can be arranged within the heat accumulator housing. For example, at least five, or more than seven or even more than ten heat pipes can be arranged in the cross section of the exhaust pipe radially circumferentially.

According to another advantageous feature of the present invention, several of the heat pipes can extend in parallel relationship within the heat accumulator housing and can be united in an end zone of the heat accumulator housing. As a result, several heat pipes which are small in diameter can be used to prevent the heat accumulator housing from being overdimensioned. The use of several small heat pipes in cross section enables enough heat quantity to be carried off from the heat accumulator and supplied to a respective heat sink in the region of the outlet of the heat accumulator housing via at least a central heat conduction in the form of a heat pipe. Overall, this leads to a particularly compact concept of the exhaust system according to the present invention.

According to another advantageous feature of the present invention, the heat pipes can have an I-shaped configuration. Advantageously, the heat pipes are configured to form a closed circuit for circulation of a medium. The schematic cross sectional representation then forms a circulation circuit. Respective selection of the respective application is then implemented by considering the field of use to be expected and the heat quantity to be transferred.

According to another advantageous feature of the present invention, the heat pipes can be integrated in a closed-loop control or open-loop control. The heat transport can hereby be controlled and/or regulated by the heat pipe itself. For example, valves may be arranged in the heat pipes to regulate and/or control the heat transport within the heat pipe. In this way, the respective heat transport can be manipulated actively or through intervention of passively actuated valves. In case of cold-start performance for example, the heat pipes cause a high heat dissipation, whereas heat dissipation is minimized via the heat pipes, when the operating temperature has been reached so that the heat accumulator can be charged in an optimum manner.

According to another advantageous feature of the present invention, a thermal insulation can be formed on an outer surface area of the heat accumulator housing. Advantageously, the thermal insulation is a metal coating. As a result of thermal insulation on the outer side of the heat accumulator housing, heat dissipation to the ambient air is minimized. This ensures that the heat accumulator is able to optimally charge in the operating behavior and the stored heat quantity can be maintained over a longest possible time period without being wasted through dissipation to the ambient air. The thermal insulation may also be implemented in the form of a thermal insulating material, air gap insulation and/or in the form of a metallic film coating. In particular, it is possible to provide a reflection of heat energy in the heat accumulator by the surface of the metallic coating back into the heat accumulator. This, too, minimizes dissipation of the heat quantity to the ambient air.

According to another advantageous feature of the present invention, a valve can be arranged on the heat accumulator housing for controlling a thermodynamic state in the heat accumulator housing. Advantageously, the thermodynamic state of a zeolite can be regulated and/or controlled via a controllable and regulatable valve.

To enrich a zeolite with water molecules, the valve may, for example, be actively opened. The valve or an additional valve may be configured as a pressure relief valve for drying the zeolite.

BRIEF DESCRIPTION OF THE DRAWING

Other features and advantages of the present invention will be more readily apparent upon reading the following description of currently preferred exemplified embodiments of the invention with reference to the accompanying drawing, in which:

FIG. 1 is a cross sectional representation of an exhaust system according to the present invention; and

FIG. 2 is a side view of an exhaust system according to the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Throughout all the figures, same or corresponding elements may generally be indicated by same reference numerals. These depicted embodiments are to be understood as illustrative of the invention and not as limiting in any way. It should also be understood that the figures are not necessarily to scale and that the embodiments are sometimes illustrated by graphic symbols, phantom lines, diagrammatic representations and fragmentary views. In certain instances, details which are not necessary for an understanding of the present invention or which render other details difficult to perceive may have been omitted.

Turning now to the drawing, and in particular to FIG. 1, there is shown an exhaust system according to the present invention, generally designated by reference numeral 1. The exhaust system 1 includes an internal exhaust pipe 2 and a heat accumulator housing 3 in surrounding relationship to the exhaust pipe 2. Exhaust gas A flows in the exhaust pipe 2 and carries off heat energy contained in the exhaust pipe 2 by way of heat transfer W into the heat storage medium 4 of the heat accumulator housing 3. Currently preferred is the use of zeolite as heat storage medium. Heat pipes 5 are arranged in the heat accumulator housing 3 to absorb heat stored in the heat storage medium 4 and to transport it away. Advantageously, the heat accumulator housing 3 is provided with an insulating layer 6 upon an outer surface area 6.

FIG. 2 shows a greatly simplified side view of the exhaust system 1. The heat accumulator housing 3 has integrated therein three heat pipes 5 of I-shaped configuration. The heat pipes 5 are arranged in parallel relation to the exhaust-gas flow direction S in the heat accumulator housing 3. The heat pipes 5 are united at an end zone 8 of the heat accumulator housing 3 to form a central heat pipe 9 by which heat energy carried away by the heat pipes 5 from the not shown heat accumulator to an unillustrated heat consumer. The heat accumulator housing 3 is further provided with a valve 10 for regulating and controlling the thermodynamic state of the heat storage medium 4. In this way, heat quantity to be carried off via the heat pipes can be regulated and controlled.

While the invention has been illustrated and described in connection with currently preferred embodiments shown and described in detail, it is not intended to be limited to the details shown since various modifications and structural changes may be made without departing in any way from the spirit and scope of the present invention. The embodiments were chosen and described in order to explain the principles of the invention and practical application to thereby enable a person skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated.

What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims and includes equivalents of the elements recited therein: 

1. An exhaust system for a combustion engine, said exhaust system comprising: an exhaust pipe; a heat accumulator housing in surrounding relationship to the exhaust pipe; and heat pipes arranged in the heat accumulator housing to provide a heat transport of heat energy contained in exhaust gas.
 2. The exhaust system of claim 1, wherein the exhaust pipe is completely encircled by the heat accumulator housing.
 3. The exhaust system of claim 1, wherein the heat accumulator housing is made of a zeolite.
 4. The exhaust system of claim 1, wherein the heat accumulator housing contains a heat storage medium.
 5. The exhaust system of claim 1, wherein the heat storage medium is made of a material that includes zeolite.
 6. The exhaust system of claim 3, wherein the heat pipes are arranged in the zeolite.
 7. The exhaust system of claim 3, wherein the heat pipes are completely enclosed by the zeolite.
 8. The exhaust system of claim 1, wherein the heat pipes are arranged in parallel relationship to an exhaust-gas flow direction.
 9. The exhaust system of claim 1, wherein several of the heat pipes extend in parallel relationship within the heat accumulator housing and are united in an end zone of the heat accumulator housing.
 10. The exhaust system of claim 1, wherein the heat pipes have an I-shaped configuration.
 11. The exhaust system of claim 1, wherein the heat pipes are configured to form a closed circuit for circulation of a medium.
 12. The exhaust system of claim 1, wherein the heat pipes are integrated in a open-loop control or closed-loop control.
 13. The exhaust system of claim 1, further comprising a thermal insulation formed on an outer surface area of the heat accumulator housing.
 14. The exhaust system of claim 12, wherein the thermal insulation is a metal coating.
 15. The exhaust system of claim 1, further comprising a valve arranged on the heat accumulator housing for controlling a thermodynamic state in the heat accumulator housing.
 16. The exhaust system of claim 15, wherein the valve is configured as a pressure relief valve.
 17. The exhaust system of claim 15, wherein the valve is integrated in an open-loop control or closed-loop control. 